The field of the invention is that of thermostat control units. More specifically, the field is that of thermostats having visual displays.
A variety of thermostatic control units serve to control data entry and display for temperature regulating systems. Examples of thermostat control units can be found in U.S. Pat. Nos. 4,264,034 (Hyltin), 4,319,711 (Barker), 4,373,664 (Barker), and 4,460,125 (Barker). A basic thermostat control has a temperature setting device for a home owner to indicate a desired ambient temperature. A thermostat also contains a heat sensing element which senses or measures the actual ambient temperature. The thermostat compares the ambient measured temperature with the desired temperature and cycles a single speed heating or cooling system on and off according to the disparity between the measured and desired temperatures. With the addition of microprocessing circuitry in a thermostat, more complicated functions become possible. For example, a home owner may specify different desired temperatures for different times of the day. Similarly, different desired temperatures for different days of the week may also be specified.
A thermostat normally provides a visual indication of both the measured ambient temperature and the home owner desired temperature. In older systems, the thermostat presents the desired temperature on a thermometer dial controlled by the homeowner. Also, the thermostat displays the observed ambient temperature on another thermometer dial, but one which is controlled by temperature sensing elements within the thermostat. Microprocessor controlled thermostats often display the temperature settings electronically with light emitting diodes (LED) or liquid crystal displays (LCD).
Thus, the general design of a thermostat is well known in the art. Variations upon the thermostat have been made for diagnostic and evaluation purposes. U.S. Pat. 4,146,085 (Wills) describes such a diagnostic thermostat. The system described in Wills has single lights which indicate the activity or inactivity of various components of its heat pump. Additionally, the Wills device has an ohm meter to check various sensors and also provide an indication of the temperature at various points in the system.
Another thermostat is described in U.S. Pat. No. 4,685,675 (Hart). The Hart thermostat shows the efficiency of a heating system. The Hart system computes efficiency as a function of the amount of BTU's supplied per degree day. The Hart thermostat has sensors which measure the inside and the outside temperatures. The difference between these two temperatures indicates the amount of work required to maintain the ambient temperature at the desired temperature. The Hart device requires a test period of operation to determine the normative system behavior. After determining the norm,. the Hart thermostat compares the efficiency of the unit in the current period with its normal efficiency. The Hart thermostat then numerically displays the efficiency on the thermostat face.
In addition, a thermostat used to measure efficiency is described in U.S. Pat. No. 4,296,727 (Bryan). The Bryan thermostat also numerically displays efficiency, but in terms of fuel consumption by the heating apparatus. In addition, the Bryan thermostat displays the smoke density in the stack. Both values are numerically displayed on a seven segment digital type of LED or LCD device.
None of these prior art devices are well adapted to use with a variable speed temperature control system. In a variable speed temperature control system, the prime movers of the system, i.e. the speeds of the compressor and blower motor, are variable and the temperature control elements work constantly. While a home owner expects the conventional single speed heating/cooling system to cycle on and off, cycling is not the case with the variable speed system. Instead of a period of operation followed by a period of non-operation, the variable speed system works at a fairly uniform level of activity. Without additional information, a home owner or a service man has no indication of the level of the system function. If a home owner does not notice the operation of the unit, then the home owner may conclude the unit is not working. Conversely, a home owner who notices the constant operation of the unit may conclude that the unit is not functioning properly because it does not cycle on and off. What is needed in the art is a thermostat which indicates the current speed of a variable speed temperature control system to provide an indication that the system is operative. In addition, what is needed in the art is a thermostat which displays the system operation graphically.